1. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing the same; and more specifically, to a semiconductor device that has a gate insulating film formed on a silicon substrate, and a gate electrode formed on the gate insulating film, and method for manufacturing such a semiconductor device.
2. Background Art
In recent years, the high integration in semiconductor integrated circuit devices has significantly proceeded, and in MOS (metal oxide semiconductor) devices, the miniaturization and raising the performance of elements, such as transistors) have been tried. Especially, the reduction of the thickness of a gate insulating film, which is one of elements composing the MOS structure, has rapidly proceeded to cope with the miniaturization, higher-speed and lower-voltage operation of transistors.
As a material for composing a gate insulating film, a SiO2 (silicon dioxide) film has conventionally been used. On the other hand, as the thickness of the gate insulating film has been reduced concurrent with the miniaturization of the gate electrode, tunnel current, or gate leakage current, caused by the direct tunneling of carriers (electrons and holes) through the gate insulating film will increase. For example, ITRS (International Technology Roadmap for Semiconductors) requires that a gate insulating film has a silicon-dioxide-film-converted thickness (or EOT (equivalent oxide thickness)) of 1.2 nm to 1.6 nm by 2007, which is considered to be the 65-nm generation). However, since gate leakage current caused by tunnel current will exceed the acceptable value when a SiO2 film is used, the adoption of a new material that can substitute the SiO2 film will be required.
Therefore, the use of a material having a higher specific dielectric constant that can substitute for the SiO2 film has been studied. The examples of presently noticeable insulating films having high dielectric constants (hereafter referred to as high-k films) include a HfO2 (hafnium dioxide) film, a HfAlOx (hafnium aluminate) film and a HfSiOx (hafnium silicate) film (refer to Patent References 1 and 2, and Non-Patent References 1 to 6).
[Patent Document 1]
U.S. Pat. No. 6,291,867 B1
[Patent Document 2]
U.S. Pat. No. 6,020,243
[Non-Patent Document 1]
H. Y. Yu et al., Applied Physics Letters, (US), 2002, Vo. 81, No. 2, pp. 376–378
[Non-Patent Document 2]
W. Zhu et al., Technology Digest of IEDM, 2001, pp. 463–466
[Non-Patent Document 3]
A. L. P. Rotondaro et al., Technology Digest of 2002 Symposium on VLSI Technology, 2002, pp. 148–149
[Non-Patent Document 4]
S. Inumiya et al., Technology Digest of 2003 Symposium on VLSI Technology, 2003, pp. 17–18
[Non-Patent Document 5]
T. Watanabe et al., Technology Digest of 2003 Symposium on VLSI Technology, 2003, pp. 19–20
[Non-Patent Document 6]
A. Morioka et al., Technology Digest of 2003 Symposium on VLSI Technology, 2003, pp. 165–166
In the above-described high-k films, the HfO2 film has a high specific dielectric constant. However, since HfO2 has poor heat resistance, there has been a problem of crystallization during the manufacture of a CMOS (complementary MOS), causing increase in leakage current and lowering the reliability of elements. On the other hand, since HfAlOx and HfSiOx have higher crystallizing temperatures, the above-described problem can be solved.
When the specific dielectric constants of SiO2 and Al2O3 are compared, that of SiO2 is about 4, while that of Al2O3 is about 9. Therefore, when the content of Hf is constant, the HfAlOx film has a higher specific dielectric constant than the HfSiOx film. For this reason, when the physical thicknesses of these films are same, the equivalent oxide thickness of the HfAlOx film can be reduced compared with the HfSiOx film. However, there has been a problem in the HfAlOx film that when the film thickness is reduced, the film quality is lowered.
On the other hand, the carrier mobility and the ON-current value in the transistor using the HfSiOx film is larger than those in the transistor using the HfAlOx film. The hysteresis observed in the capacity-voltage curve of a transistor using the HfSiOx film is smaller than that in the transistor using the HfAlOx film. Therefore, the trap of electrons in the boundary and the film in the HfSiOx film is less. However, as described above, since the HfSiOx film has a lower specific dielectric constant than the HfAlOx film, there has been a problem that the equivalent oxide thickness cannot be reduced.